小柯机器人

科学家发现第一个恐龙蛋原来是软的
2020-06-18 22:20
美国自然博物馆Mark A. Norell、耶鲁大学Jasmina Wiemann、Matteo Fabbri等研究人员合作发现,第一个恐龙蛋原来是软的。2020年6月17日,《自然》杂志在线发表了这一研究成果。
 
通过矿物学、有机化学和超微结构的证据,研究人员证明了保存良好鸟臀目恐龙原角龙和蜥脚类鼠龙的蛋壳具有非生物矿化的软壳性质。对一组代表性的硬壳和软壳、化石和现存的双孔亚纲蛋壳的原位拉曼光谱统计评估表明,原本有机但二次磷化的原角龙和有机的鼠龙蛋壳与柔软的、未生物矿化的蛋壳聚类在一起。组织学证实了这些甲壳类恐龙蛋的有机组成,并揭示出类似于乌龟软壳的分层排列。
 
通过祖先状态的成分和超微结构重建,研究人员将原角龙和鼠龙的蛋壳与其他双足动物的蛋壳进行了比较,从而揭示了第一个恐龙蛋是软壳的。在整个中生代,钙化的硬壳恐龙蛋至少独立进化了三次,这解释了化石记录中对恐龙蛋壳的偏差认知。
 
据了解,钙化的蛋壳可保护发育中的胚胎免受环境压力,并有助于生殖成功。由于现代鳄鱼和鸟类产下硬壳蛋,这种蛋壳类型已被推断为非禽类恐龙所有。已知恐龙蛋壳的特征是:最内层的膜、含有方解石的蛋白质覆盖基质以及最外层的蜡状角质层。钙质蛋壳由一个或多个超微结构层组成,在三个主要的恐龙进化枝之间,呼吸孔的构造也明显不同。到目前为止,仅发现了鸭嘴龙、几种蜥脚类和坚尾龙类的蛋壳。化石记录的匮乏和中间蛋壳类型的缺失挑战所有恐龙蛋壳结构具有一致性的观点。
 
附:英文原文

Title: The first dinosaur egg was soft

Author: Mark A. Norell, Jasmina Wiemann, Matteo Fabbri, Congyu Yu, Claudia A. Marsicano, Anita Moore-Nall, David J. Varricchio, Diego Pol, Darla K. Zelenitsky

Issue&Volume: 2020-06-17

Abstract: Calcified eggshells protect developing embryos against environmental stress and contribute to reproductive success1. As modern crocodilians and birds lay hard-shelled eggs, this eggshell type has been inferred for non-avian dinosaurs. Known dinosaur eggshells are characterized by an innermost membrane, an overlying protein matrix containing calcite, and an outermost waxy cuticle2,3,4,5,6,7. The calcitic eggshell consists of one or more ultrastructural layers that differ markedly among the three major dinosaur clades, as do the configurations of respiratory pores. So far, only hadrosaurid, a few sauropodomorph and tetanuran eggshells have been discovered; the paucity of the fossil record and the lack of intermediate eggshell types challenge efforts to homologize eggshell structures across all dinosaurs8,9,10,11,12,13,14,15,16,17,18. Here we present mineralogical, organochemical and ultrastructural evidence for an originally non-biomineralized, soft-shelled nature of exceptionally preserved ornithischian Protoceratops and basal sauropodomorph Mussaurus eggs. Statistical evaluation of in situ Raman spectra obtained for a representative set of hard- and soft-shelled, fossil and extant diapsid eggshells clusters the originally organic but secondarily phosphatized Protoceratops and the organic Mussaurus eggshells with soft, non-biomineralized eggshells. Histology corroborates the organic composition of these soft-shelled dinosaur eggs, revealing a stratified arrangement resembling turtle soft eggshell. Through an ancestral-state reconstruction of composition and ultrastructure, we compare eggshells from Protoceratops and Mussaurus with those from other diapsids, revealing that the first dinosaur egg was soft-shelled. The calcified, hard-shelled dinosaur egg evolved independently at least three times throughout the Mesozoic era, explaining the bias towards eggshells of derived dinosaurs in the fossil record.

DOI: 10.1038/s41586-020-2412-8

Source: https://www.nature.com/articles/s41586-020-2412-8

Nature:《自然》,创刊于1869年。隶属于施普林格·自然出版集团,最新IF:69.504
官方网址:http://www.nature.com/
投稿链接:http://www.nature.com/authors/submit_manuscript.html


本期文章:《自然》:Online/在线发表

分享到:

0